The campaigner's fiancee Cynthia Kelley discovered his body at the bottom of the pool at their home in Rialto, California early on Sunday morning (17Jun12), according to TMZ.com.
Police officers were called to the scene and removed King from the water. They attempted to resuscitate him to no avail and he was taken to a local hospital, where he was pronounced dead at 6.11am local time.
King became infamous as the victim of a brutal beating by four Los Angeles police officers in 1991. The assault was caught on camera but the cops were acquitted by a jury and the ruling sparked the L.A. Riots.
He recently revisited the harrowing incident on various news programmes to mark the 20th anniversary of the unrest and discuss a new TV documentary, Uprising: Hip-Hop & the L.A. Riots, which was narrated by rapper Snoop Dogg and aired in America last month (May12).
King struggled with drug and alcohol issues in recent years and sought treatment on U.S. reality shows Celebrity Rehab with Dr. Drew and its spin-off, Sober House.
Police have ruled out foul play and are investigating his death as a drowning case.